Mechanical oscillators



July 8, 1958 c. F. CLIFFORD MECHANICAL OSCILLATORS Original Filed July 10 1951 ATrORNEYs MECHANICAL QSCILLATORS Cecil l ranlr Clifford, Bath, England Uriginal application July 16, 1951, Serial No. 236,019, new Patent No. 2,743,614, dated May 1, 1956. Divided and this application January 30, 1956, Serial No. 562,338

Claims priority, application Great Britain July 15, 1950 It Claims. (Cl. 74-1.5)

This invention relates to mechanical oscillators, and is particularly applicable to magnetic escapernent mechanisms of the kind in which relatively rotatable and oscillatable parts are coupled together by means of a magnetic coupling, the oscillatable part being subject to a restoring force, giving a natural frequency of oscillation with substantial isochronism. Several examples of magnetic escapement mechanisms of the kind referred to are described in prior United States Patents Nos. 2,554,523, 2,616,298 and 2,690,646.

This application is a division of my pending application, Serial No. 236,019, filed July 10, 1951.

The expression magnetic coupling is used herein to define the coupling between the aforesaid relatively movable parts wherein the motion of rotation is coupled at all times to the motion of oscillation my magnetic fiux between at least one pole-shaped member and a wavy track whereby the combined relative rotational and oscillatory movement of the parts results in the relative following of such track by the said pole-shaped member so as to provide the pre-requisite condition of escape ment in which the frequency of oscillation determines the speed of rotation.

If an oscillating part is carried by a resilient member, such as a reed, the resilience of which provides the restoring force for oscillation, and if due regard is paid to keeping stresses in such resilient member reasonably low, then as the returning force is substantially directly proportional to displacement a reasonably isochronous oscillatable assembly is formed, i. e. the frequency of oscillation is substantially the same for all amplitudes complying with such regard.

In a wavy track type of magnetic escapement as hitherto known, the wavy track was constructed with a uniform dimensional factor, that is to say of uniform width and distance relative to the complementary magnetic pole so as to give, as far as possible, a magnetic coupling of uniform intensity throughout the range of relative movement of said parts. The present invention is based upon the appreciation that when as oscillatable assembly is magnetically coupled to a driving member by any of the uniformly dimensioned and non-compensated means proposed to date, an error is introduced through parasitic magnetic forces, which expression is explained below, superimposed on the restoring force of the oscillatable assembly, with consequent departures from isochronism. Other forces inimical to isochronism are herein termed other parasitic forces. It is of course necessary in any escapement for the rotary motion to impulse the oscillatory motion, so as at least to maintain, if not also to initiate, the oscillation of the oscillatory assembly and consequently such impulsing is a force superimposed on the restoring force of the oscillatory system; but such impulsing force is a known and rela tively calculable factor having little effect on isochronism. in contradistinction to the impulsing force, the shape of some forms of wavy track and complementary poleatent. G

f atentecl July 8, 1958 shaped members, convenient for manufacture and heretofore known, are such that in their relative positions during escapement, the magnetic coupling they provide has a force component, hereinafter termed a parasitic magnetic force, superimposed on the restoring force and which has hitherto been of an order capable of substantial interference with isochronism.

According to the invention a magnetic eseapernent mechanism (having relatively rotatable and oscillatable parts, the latter subject to a restoring force giving substantial isochronism, coupled together by means of a magnetic coupling) of the kind referred to, is characterized by means for reducing anisochronism due to magnetic and other parasitic forces as hereinbefore defined.

According to a first embodiment of the invention means are provided for substantially eliminating the said parasitic magnetic forces.

According to a second embodiment of the invention a construction is provided whereby the said parasitic forces obey the isochronous law that its component superimposed on the restoring force is proportional to deflection, so that the combined restoring force substantially obeys such law.

In the accompanying drawings:

Fig. 1 is a perspective view of an escapement embody ing the invention according to the embodiment first described above;

Fig. 2 is a sectional view on line 2--2 of Fig. 1;

Fig. 3 is a modified form of rotor illustrating the same embodiment as is illustrated in Fig. 1;

Fig. 4 is a perspective view of an escapement mechanism illustrating the second embodiment of my invention; and

Fig. 5 is a sectional view illustrating another form of escape wheel or rotor which may be employed in the second embodiment of the invention.

As one example of the first embodiment aforesaid for substantially eliminating the parasitic forces on say, the wavy tracks and extensions thereof the track, according to the present invention could, for example, be made thinner at the wavy track than at the extensions so that by reason of a larger air gap the centralizing component of the magnetic coupling is substantially eliminated, i. e. the pole-shaped parts are no more attracted to this portion than to the extensions. As another example of such first embodiment, the wavy track part could be made less wide than the extensions but this has an adverse effect on the self-starting properties of the escapement.

As shown in Figs. 1 and 2, there are separate rotatable and oscillatable parts, the rotatable part consisting of a wheel or rotor having spokes 10 having arched apertures 11, and radially in line with the arched apertures are outer tooth-like projections 12 which are separated by U-shaped notches 13, the arches 11 and U-shaped notches 13 being so proportioned as to form a wavy track to which the spokes 10 and tooth-like projections 12 form relatively radial extensions.

As can be seen in the drawing, an annular groove 14 is provided at one side of the rotor, this groove producing rebates 15 and 16 on the spokes and projections respectively. As is also shown in the drawing: on dotted lines, the mean wavy track consists of a series of Y-shaped track paths alternately in opposite directions. The tails 17 and 18 respectively of the Ys form the inner and outer extensions of the track, and the arms 1"? collectively form the track itself.

Associated with the rotary member is shown the oscillatory system consisting of a magnet 2i having inwardly directed pole formations 21 which are in opposed relation to the opposite faces of the rotor. The magnet is re siliently suspended from a fixed bracket 22 by a spring 23, the latter being secured to the arch or bight portion of the magnet, and the line of support of the magnet being substantially at the center of gravity of the magnet and spring assembly. The annular groove or rabbet 14 may be formed by machining away some of the thickness of the rotor, particularly at the wavy track portion, and this has been found to reduce substantially the parasitic forces. While such machining is shown at one side only of the rotor, it can obviously be provided at both sides, and the resultant enlargement of the air gap at such portion of the track removes within the limit of practical approximation the centralizing force which would otherwise obtain.

As shown in Fig. 3, the rotor compared with that illustrated in Fig. 1 has the arches 11 and the U-shaped notches 13 relatively deeper so that the centers of the wavy track portions where the arms of the Y-shaped track sections join, as indicated at 24, are narrower so as to decrease the attraction to the poles of the vibratory system at the central position for such assembly. That is to say, the rotor exerts a lesser restoring force upon the poles of the magnet adjacent the central'position of the latter than would otherwise obtain due to the narrower dimension of the magnetic wavy track sections of the rotor.

However, the magnet poles 21, with such construction, overlap the width of such narrow section of the rotor, making the magnet reluctant to cross this section, and hence adversely affecting the self-starting properties of the escapement. Thus narrowing the track to reduce the section at the junction of the tail and arms of the Y-shaped portions of the track, while substantially eliminating magnetically generated centralizing forces, sufiicient to eliminate parasitic forces, has the aforesaid disadvantage that the portions at 24 may be narrower than is desirable.

It will be apparent that both the arrangements of Fig. 1 and Fig. 3 provide substantial elimination of the parasitic magnetic forces by so shaping the rotor as to substantially eliminate centralizing forces previously present, this shaping being effected by varying the dimensions of the rotor.

As an example of the second embodiment of isochronizing the parasitic forces according to this invention, the driving magnetic track and its extensions are so shaped that the restoring force (due to the parasitic magnetic forces) applied to the oscillator obeys the law that the magnetic restoring forces are substantially proportional to the deflection. The shaping of the track can consist, for instance, of tapering the thickness or width of the track or of tapering or varying the thickness of material of which the rotor is formed.

As shown in Fig. 4, a rotor suitable for use with the vibratory system such, as shown in Fig. l, is made with spokes 26 and toothlike projections 27 of tapered shape. That is to say, both the spokes and toothlike projections are considerably broader at their junction with the wavy track than farther away from such junction, but they are of uniform thickness from face to face of the wheel. That is to say that the bases of the toothlike projections 27 are considerably broader than the free ends thereof, and likewise the outer ends of the spokes are considerably broader in a circumferential direction than are the inner ends. The thickness of the material of which the rotor is made, however, is uniform throughout. The oscillating magnet 2%, spring 29 and supporting member Stl are of the form described previously in connection with the corresponding parts illustrated in Fig. 1, and preferably here also the magnet and spring will be supported at substantially the center of gravity of this assembly.

A further construction illustrating the second embodiment of the invention is shown in Fig. 5 in which the spoke portions 32 and the toothlike projections 33 are of tapered shape with their thicker ends joining the wavy magnetic track zone 34. The variation in the dimension or shape of these parts in this plane (at right angles to the shaping shown in Fig. 4) has the same effect as that shown in Fig. 4 in that it provides, compared with a rotor not so shaped, an increased parasitic or superimposed returning force acting to centralize the vibratory system with the shaping so proportioned that such superimposed returning force substantially obeys the law for isochronism. That is to say, such returning force is substantially directly proportional to displacement.

Escapement mechanism of the kind referred to generally can be improved by either of the methods aforesaid or by a combination of such methods.

Obviously, while carrying out the invention for the removal of isochronous errors arising from parasitic magnetic forces the modification adopted may depart slightly from absolute correction of the parasitic magnetic force so as to compensate also for other known factors causing errors of isochronism, such departure being within the scope of the present invention. For instance, it has also been found that with no escape wheel present, if the oscillator is deflected by hand and then released, the vibrations as they die down change in frequency, being usually faster on the smaller amplitudes. Such errors of isochronism due to forces other than parasitic magnetic forces, can be compensated by any of the means above described.

While I have shown and described some embodiments of my invention, it will be understood that it is not to be limited to all of the details shown, but is capable of modification and variation within the spirit of the invention and within the scope of the claims.

What I claim is:

l. A magnetic escapement mechanism embodying an oscillating member having a position of repose intermediate its extreme positions during oscillation, and a complernentary rotating member, said rotary member presenting a wavy magnetic track thereon, said oscillating member having at least one pole face thereon and being subject to a restoring force giving substantial isochronism, and said members being coupled together by a magnetic coupling wherein the motion of rotation is coupled at all times to the motion of oscillation by the magnetic flux between said pole face and the wavy track, and said wavy track being constructed with a nonuniform dimensional factor, the departure from uniformity being such that the centralizing force of the magnetic coupling adjacent the repose position of the oscillating member is varied with respect to that exerted at its extreme positions as to reduce anisochronism due to mag- 1 netic and other parasitic forces.

2. A magnetic escapement mechanism according to claim 1 wherein the nonuniform dimensional factor is such as to eliminate magnetic and other parasitic forces.

3. A magnetic escapement mechanism as in claim 1 I wherein the nonuniform dimensional factor is such as to render the parasitic, magnetic and other forces directly proportional to the displacement of the oscillating member so that the combined restoring force effects substantial isochronous movement of the oscillating member.

4. A magnetic escapement mechanism as in claim 1 wherein the wavy track is of nonuniform width relatively to the pole face of the complementary oscillating member, the departure from uniformity being such as to eliminate magnetic and other parasitic forces.

5. A magnetic escapement mechanism as in claim 1 wherein the wavy track is at a nonuniform distance from the pole face of the complementary oscillating member, the departure from uniformity being such as to eliminate magnetic and other parasitic forces.

6. A magnetic escapement mechanism as in claim 1 wherein said rotating member is provided with projections on its periphery, and said projections are of lesser thickness adjacent the wavy track than at portions remote therefrom.

7. A magnetic escapement mechanism as in claim 1 wherein said rotary member is provided with projections upon its periphery, and said projections are of lesser width adjacent their free ends than adjacent their bases where they join the wavy track.

8. A magnetic escapernent mechanism as in claim 1 wherein the thickness of said projections is of nonuniform dimension in a direction parallel to the axis of the member at their bases in relation to their end portions remote from the bases.

9. An escapement mechanism as in claim 8 wherein the thickness of said projections from face to face of the rotary member is less at their end portions than adjacent the wavy track.

10. A magnetic escapement mechanism as in claim 1 wherein the rotary member is provided with projections upon its periphery and spokes extending outwardly from the axis, and the wavy track portion is of narrower width between the outer ends of the spokes and bases of the propections than at other points.

References Cited in the file of this patent UNITED STATES PATENTS Clifford Oct. 9, 1951 2,642,274 Andresen June 16, 1953 

